Development of a Polymerase Chain Reaction to Differentiate Avian Leukosis Virus (ALV) Subgroups: Detection of an ALV Contaminant in Commercial Marek's Disease Vaccines

Simultaneous Detection of Three Subgroups of Avian Leukosis Virus Using the Nanoparticle-Assisted PCR Assay

Nanoparticle-assisted polymerase chain reaction (nanoPCR) is a novel method for the rapid detection of pathogens. A sensitive and specific multiple nanoPCR assay was developed for simultaneous detection of avian leucosis virus (ALV) subgroups A, B and J. In this study, three pairs of primers were designed, based on the conserved region of the gp85 gene. An exploration of the optimal primer concentration and annealing temperature were carried out, for better performance of the nanoPCR assay. According to the results, the multiple nanoPCR assay amplified 336 pb, 625 bp and 167 bp fragments of ALV-A, -B and -J, respectively, and showed no cross-reactivity with irrelevant pathogens, suggesting the excellent specificity of the assay. The constructed standard DNA templates were used to estimate the limit of detection. As shown by the results, the detection limit of the nanoPCR assay was nearly 10 copies/μL. To further evaluate the detection ability of the assay, 186 clinical samples were detected using the nanoPCR assay, among which, 14 samples were confirmed as ALV positive; the results were further confirmed by sequencing. In conclusion, a highly specific and sensitive nanoPCR assay was successfully developed, which could be a useful tool for clinical diagnosis as well as for the discrimination of ALV-A, -B and -J.

Intrahepatic Cholangiocarcinoma Identified in a Zoo-Housed Sandhill Crane (Grus canadensis): An Anatomopathological and Metagenomic Study

Tumors in birds can be caused by a variety of factors such as species, age, sex, virus, chemicals, and environment. In particular, tumors are a major cause of death in long-lived birds such as parrots and zoo birds. A male sandhill crane that was bred for 8 years in a zoo was diagnosed with intrahepatic cholangiocarcinoma (ICC). At necropsy, the liver revealed a multinodular mass of variable colors, and severe cirrhosis and hemorrhages were present. Histologically, ICC was characterized by the presence of both types of ICC: small-duct type and large-duct type. Large-duct-type ICC was distinguished by the presence of multifocal biliary neoplasia, characterized by the diffuse papillary proliferation of columnar cells resembling large cholangiocytes. Small-duct-type ICC was characterized by the presence of non-mucin-producing cuboidal cells such as bile duct cells. In this case, no viral cause was identified from the metagenomic analysis and PCR of ICC; however, a contributing role of Cutibacterium sp. and E. coli identified from the metagenomics could not be excluded. This study is the first to describe the anatomopathological characteristics of ICC in the studied sandhill crane and attempts to determine its potential infectious etiology using metagenomics.

Avian Leukosis: Will We Be Able to Get Rid of It?

Avian leukosis viruses (ALVs) have been virtually eradicated from commercial poultry. However, some niches remain as pockets from which this group of viruses may reemerge and induce economic losses. Such is the case of fancy, hobby, backyard chickens and indigenous or native breeds, which are not as strictly inspected as commercial poultry and which have been found to harbor ALVs. In addition, the genome of both poultry and of several gamebird species contain endogenous retroviral sequences. Circumstances that support keeping up surveillance include the detection of several ALV natural recombinants between exogenous and endogenous ALV-related sequences which, combined with the well-known ability of retroviruses to mutate, facilitate the emergence of escape mutants. The subgroup most prevalent nowadays, ALV-J, has emerged as a multi-recombinant which uses a different receptor from the previously known subgroups, greatly increasing its cell tropism and pathogenicity and making it more transmissible. In this review we describe the ALVs, their different subgroups and which receptor they use to infect the cell, their routes of transmission and their presence in different bird collectivities, and the immune response against them. We analyze the different systems to control them, from vaccination to the progress made editing the bird genome to generate mutated ALV receptors or selecting certain haplotypes.

Simultaneous detection and differentiation of three oncogenic viral diseases of chicken by use of multiplex PCR

Avian oncogenic or tumor diseases are common in poultry industry causing significant economic loss. Marek's disease (MD), avian leukosis (AL) and Reticuloendotheliosis (RE) are the three major viral oncogenic infections that are difficult to differentiate with gross lesions. Multiplex PCR for simultaneous detection and differentiation of these three viruses was developed and validated. The primers targeting the genes of pp38, pol and LTR for MDV, ALV and REV were designed to yield 206, 429, and 128 bp, respectively. The sensitivity of the PCR primers was checked with serial dilution of positive template DNA for each virus and found to be in the range of 10^-5 to 10^-7 of 1 µg/µl of initial template DNA. Out of 114 suspected tumor samples screened, 8 samples were positive for MDV, 13 samples were positive for ALV and 31 samples positive for REV. Five samples were positive for both MD and ALV; 3 samples were positive for MD and REV and 25 samples were positive for ALV and REV. Eight samples were positive for all three viruses. Multiplex PCR demonstrated to be a useful technique for simultaneous, rapid detection and differentiation of major tumor causing and immunosuppressive viral diseases of chicken.

Phylogenetic analyses on Marek's disease virus circulating in Iranian backyard and commercial poultry indicate viruses of different origin

As neoplastic viruses have been affecting Iranian chicken farms more frequently in recent years, the first step in prevention may therefore be to genetically characterize and systematically identify their source and origin. Recently, we published a phylogenetic analysis based on the meq gene of Gallid alphaherpesvirus 2, commonly known as serotype 1 Marek's disease virus (MDV-1), that circulated in Iranian backyard and commercial chickens. In the current study, we are reporting for the first time the identification of a 298 aa meq protein containing only two PPPP motifs from an MDV-1-infected unvaccinated backyard turkey. This protein length has never been reported from any turkey species before. According to phylogenetic analysis, a close genetic relationship (0.68%) to several chicken-origin isolates such as the American vv + 648A strain was found. In addition, we identified a standard meq protein from a MDV-1-infected commercial chicken farm. In corroboration with our previous finding from other Iranian provinces, it is likely that the highly identical MDV-1 viruses currently circulating in Iranian chicken farms, which may be indicative of human role in the spread of the virus, have similar Eurasian origin. Our data suggest that regardless of the meq size, MDV-1 circulating in Iran are from different origins. On the other hand, meq sequences from bird species other than chicken have been reported but are very few. Our investigation suggests MDV-1 circulating in turkey do not have species-specific sequences.

Co-infection of Marek's disease virus with different oncogenic immunosuppressive viruses in chicken flocks

Oncogenic tumour diseases are major threat to poultry industry. Marek's disease (MD), avian leukosis (ALV) and reticulosendotheliosis virus (REV) are the major tumour causing immunosuppressive viral diseases of chicken. A total of 120 tissue samples presented with tumour lesions from different chicken flocks of coloured broiler, layer breeders and native chicken breeds were screened for MDV, ALV and REV by histopathology and virus specific PCRs individually. Presence of oncogenic viruses in the samples were screened by virus specific PCR. A total of 47 samples were detected either with single infection or dual infection with these viruses. Out of 47, 17 were detected with either one of the viruses and remaining 30 with any of the two viruses. REV was the major cause of tumour in the present samples followed by MDV. ALV was not detected alone, it was either with MD or REV. All 5 ALV positive samples were detected with ALV-E subtype. REV was detected predominantly (22 out of 25 positives) as single infection rather than co-infection.

Retroviral Association with Ovarian Adenocarcinoma in Laying Hens

The laying hen has been used as a model for ovarian adenocarcinoma (OAC) in women. Previous work has shown an association between expression of endogenous retroviral proteins and elevated envelope mRNA and occurrence of OAC has been demonstrated in humans, but causality has not been demonstrated. The objective of this study was to determine whether there is a similar association between retrovirus presence and OAC in a commercial laying hen flock at the University of Illinois Poultry Research facility with a history of a high prevalence of OAC in its aged hens. Laying hens of three age strata were randomly selected for a cross-sectional study. Blood samples were collected, and serum was tested for antigens of endogenous or exogenous avian leukosis virus (ALV) by ELISA. Birds were humanely euthanized, and spleens, ovaries, and any tissues with gross lesions were sampled. Ovaries and tissues with gross lesions were examined histologically and spleens were used for RT-PCR to detect endogenous ALV via ALV-E env mRNA expression. Overall, hens with OAC were 5.2 times more likely to be ALV positive than hens without OAC (95% C.I. = 2.06-13.14). Holding age stratum constant, OAC positive hens were 3.6 times more likely to be positive for ALV via antigen-capture ELISA (95% C.I. 1.08- 11.96). Endogenous ALV-E in hens may be analogous to the human endogenous retroviruses, which have also been associated with OAC in women. Further studies to establish causation are warranted to better understand the potential for laying hens to serve as a laboratory model for viral-induced ovarian tumors in humans.

Spontaneous Avian Erythroblastosis in a Chicken Confirmed by Immunohistochemical Detection of Hemoglobin in Tumor Cells

Avian erythroblastosis (AE; erythroid leukosis) was detected in a 78-day-old Japanese native chicken. At necropsy, the liver was enlarged and diffusely dark red in color. Moderate splenomegaly was observed. Histologically, round to polygonal tumor cells were observed only in the blood vessels of the liver and other organs. Immunohistochemistry (IHC) was performed on formalin-fixed, paraffin-embedded (FFPE) sections to characterize tumor cells. Tumor cells, as well as normal erythrocytes as positive controls, were consistently positive for IHC by using the commercially available anti-human hemoglobin antibody. Exogenous avian leukosis virus (ALV) subgroup B and endogenous ALV-E genes were detected by PCR, although ultrastructural observation revealed no viral particles associated with tumor cells. Results suggest that the commercial anti-human hemoglobin antibody used in the study cross-react to chicken erythrocytes on FFPE sections by IHC and can also be used for definitive diagnosis of the spontaneous case of AE in chickens.

Genetic evolution of Marek's disease virus in vaccinated poultry farms

Background and Aim:

The Marek’s disease virus (MDV) is a neoplastic disease causing serious economic losses in poultry production. This study aimed to investigate MDV occurrence in poultry flocks in the Lower Egypt during the 2020 breakout and genetically characterized Meq, gL, and ICP4 genes in field strains of MDV.

Materials and Methods:

Forty samples were collected from different breeds from eight Egyptian governorates in 2020. All flocks had received a bivalent vaccine (herpesvirus of turkey FC-126 + Rispens CVI988). However, weight loss, emaciation, reduced egg production, paralysis, and rough/raised feather follicles occurred. Samples were collected from feather follicles, liver, spleen, and nerve tissue for diagnosis by polymerase chain reaction. MDV genetic characterization was then performed by sequencing the Meq, gL, and ICP4 genes of five positive samples representing different governorates and breeds.

Results:

A total of 28 samples were positive for MDV field strains, while two were related to MDV vaccinal strains. All samples tested negative for ALV (A, B, C, D, and J) and REV. Phylogenetic analysis of the Meq gene of sequenced samples revealed that all MDVs were related to the highly virulent European viruses (Gallid herpesvirus 2 ATE and PC12/30) with high amino acid (A.A.) identity 99.2-100%. Alternatively, there was low A.A. identity with the vaccine strains CVI988 and 3004 (up to 82.5%). These results indicate that further investigation of the efficacy of current Egyptian vaccines is required. The Egyptian strains also harbor a specific mutation, allowing clustering into two subgroups (A and B). By mutation analysis of the Meq gene, the Egyptian viruses in our study had R101K, P217A, and E263D mutations present in all Egyptian viruses. Furthermore, R176A and T180A mutations specific to our strains contributed to the high virulence of highly virulent strains. There were no mutations of the gL or ICP4 genes.

Conclusion:

Further studies should evaluate the protection contributed by current vaccines used in Egypt.

Molecular characteristics of subgroup J avian leukosis virus isolated from yellow breeder chickens in Guangdong, China, during 2016-2019

Since 2005, subgroup J avian leukosis virus (ALV-J) infection has been present in yellow chickens in Guangdong, China, causing severe economic losses to the local poultry industry. ALV-J is a rapidly evolving retrovirus. To investigate the molecular characteristics of ALV-J isolates from yellow breeder chickens in Guangdong, 17 virus strains were isolated from 6549 anticoagulants from clinically healthy birds between 2016 and 2019, and completely sequenced and phylogenetically analyzed. Phylogenetic analysis of the gp85 gene showed that all isolated viruses were divided into three different branches. Notably, 41.2% (7/17) of the isolates shared a novel G2598A nucleotide mutation in the pol gene and caused the stop codon to be advanced by 8 positions. Nearly 200 nucleotides were deleted from the redundant TM (rTM) region in all strains, but all retained an intact direct repeat (DR1). 82.4% (14/17) of isolates contained a complete E element. Additionally, 29.4% (5/17) of isolates detected an 11 bp deletion in U3 region, and the AIB REP1 transcription factor is missing. The study indicated that ALV-J infection had still been prevalent in the yellow breeder chicken farms in Guangdong, and the genetic background of the strains is diverse. This study provides the latest data on the molecular characteristics of ALV-J, which will help to reveal the evolution trend of ALV-J and develop relevant prevention and control measures.

Genetic variability of the Avian leukosis virus subgroup J gp85 gene in layer flocks in Lower Egypt

Aim

This study aimed to determine the prevalence of layer flock tumor disease in Lower Egypt during the period of 2018-2019 and to undertake molecular characterization and determine the genetic diversity of all identified viruses.

Materials and Methods

Forty samples were collected from layer chicken located in six governorates of Lower Egypt during the period of 2018-2019. Samples were taken from tumors in different organs. Tumor tissues were identified by histopathological sectioning and then further confirmed by a reverse-transcription polymerase chain reaction. Finally, genetic evolution of Avian leukosis virus (ALV-J) gp85 gene was studied.

Results

All the study samples were negative for Marek's disease virus, reticuloendotheliosis virus, ALV (A,B,C and D) and 20 samples were positive for ALV-J in backyard in six governrates. Sequencing of ALV-J gp85 gene was performed for six representative samples (one from each governorate), and they were found to be genetically related to prototype virus HPRS-1003 (identity percentage: 91.2-91.8%), but they were from a different group that was similar to the AF88-USA strain (first detected in 2000) with specific mutations, and they differed from a strain that was previously isolated in Egypt in 2005, forming two different subgroups (I and II) that had mutations in the hr1domain (V128F, R136A) and hr2 domain (S197G, E202K).

Conclusion

The ALV-J virus was the main cause of neoplastic disease in layer chickens from Lower Egypt in the period of 2018-2019. We found that the genetic evolution of ALV-J gp85 gene was related to prototype virus HPRS-1003 but in a different group with a specific mutation. Further studies are needed to evaluate the antigenicity and pathogenicity of recently detected ALV-J strains.

Endogenous Avian Leukosis Virus in Combination with Serotype 2 Marek's Disease Virus Significantly Boosted the Incidence of Lymphoid Leukosis-Like Bursal Lymphomas in Susceptible Chickens

Lymphoid leukosis (LL)-like lymphoma is a low-incidence yet costly and poorly understood disease of domestic chickens. The observed unique characteristics of LL-like lymphomas are that the incidence of the disease is chicken line dependent; pathologically, it appeared to mimic avian leukosis but is free of exogenous ALV infection; inoculation of the nonpathogenic ALV-E or MDV-2 (SB-1) boosts the incidence of the disease; and inoculation of both the nonpathogenic ALV-E and SB-1 escalates it to much higher levels. This study was designed to test the impact of two new ALV-E isolates, recently derived from commercial broiler breeder flocks, in combination with the nonpathogenic SB-1 on LL-like lymphoma incidences in both an experimental egg layer line of chickens and a commercial broiler breeder line of chickens under a controlled condition. Data from this study provided an additional piece of experimental evidence on the potency of nonpathogenic ALV-E, MDV-2, and ALV-E plus MDV-2 in boosting the incidence of LL-like lymphomas in susceptible chickens. This study also generated the first piece of genomic evidence that suggests host transcriptomic variation plays an important role in modulating LL-like lymphoma formation.

In 2010, sporadic cases of avian leukosis virus (ALV)-like bursal lymphoma, also known as spontaneous lymphoid leukosis (LL)-like tumors, were identified in two commercial broiler breeder flocks in the absence of exogenous ALV infection. Two individual ALV subgroup E (ALV-E) field strains, designated AF227 and AF229, were isolated from two different breeder farms. The role of these ALV-E field isolates in development of and the potential joint impact in conjunction with a Marek’s disease virus (MDV) vaccine (SB-1) were further characterized in chickens of an experimental line and commercial broiler breeders. The experimental line 0.TVB*S1, commonly known as the rapid feathering-susceptible (RFS) line, of chickens lacks all endogenous ALV and is fully susceptible to all subgroups of ALV, including ALV-E. Spontaneous LL-like tumors occurred following infection with AF227, AF229, and a reference ALV-E strain, RAV60, in RFS chickens. Vaccination with serotype 2 MDV, SB-1, in addition to AF227 or AF229 inoculation, significantly enhanced the spontaneous LL-like tumor incidence in the RFS chickens. The spontaneous LL-like tumor incidence jumped from 14% by AF227 alone to 42 to 43% by AF227 in combination with SB-1 in the RFS chickens under controlled conditions. RNA-sequencing analysis of the LL-like lymphomas and nonmalignant bursa tissues of the RFS line of birds identified hundreds of differentially expressed genes that are reportedly involved in key biological processes and pathways, including signaling and signal transduction pathways. The data from this study suggested that both ALV-E and MDV-2 play an important role in enhancement of the spontaneous LL-like tumors in susceptible chickens. The underlying mechanism may be complex and involved in many chicken genes and pathways, including signal transduction pathways and immune system processes, in addition to reported viral genes.

IMPORTANCE Lymphoid leukosis (LL)-like lymphoma is a low-incidence yet costly and poorly understood disease of domestic chickens. The observed unique characteristics of LL-like lymphomas are that the incidence of the disease is chicken line dependent; pathologically, it appeared to mimic avian leukosis but is free of exogenous ALV infection; inoculation of the nonpathogenic ALV-E or MDV-2 (SB-1) boosts the incidence of the disease; and inoculation of both the nonpathogenic ALV-E and SB-1 escalates it to much higher levels. This study was designed to test the impact of two new ALV-E isolates, recently derived from commercial broiler breeder flocks, in combination with the nonpathogenic SB-1 on LL-like lymphoma incidences in both an experimental egg layer line of chickens and a commercial broiler breeder line of chickens under a controlled condition. Data from this study provided an additional piece of experimental evidence on the potency of nonpathogenic ALV-E, MDV-2, and ALV-E plus MDV-2 in boosting the incidence of LL-like lymphomas in susceptible chickens. This study also generated the first piece of genomic evidence that suggests host transcriptomic variation plays an important role in modulating LL-like lymphoma formation.

Geese not susceptible to virulent subgroup J avian leukosis virus isolated from chickens

To determine whether geese are susceptible to infection by avian leukosis virus (ALV), 702 serum samples from domestic and foreign goose breeds were screened for p27 antigen as well as being inoculated into DF-1 cell cultures to isolate ALV. Although 5.7% of samples were positive for p27 antigen, reactivity appeared to be non-specific because no ALV was detected in the corresponding DF-1 cultures. To further determine whether geese are susceptible to ALV-J isolated from chickens, ALV-J strain JS09GY7 was artificially inoculated into 10-day-old goose embryos, with one-day-old hatched goslings then screened for p27 antigen and the presence of ALV. In all cases, the results of both tests were negative. Liver tissues from the 1-day-old goslings were screened using a polymerase chain reaction-based assay, which failed to amplify ALV-J gene fragments from any of the samples. Further, no histopathological damage was observed in the liver tissues. ALV-J was further inoculated intraperitoneally into one-day-old goslings, with cloacal swabs samples and plasma samples then collected every 5 days for 30 days. All samples were again negative for the presence of p27 antigen and ALV, and liver tissues from the challenged geese showed no histopathological damage and were negative for the presence of ALV-J gene fragments. Furthermore, p27 antigen detection, PCR-based screening, and indirect immunofluorescence assays were all negative following the infection of goose embryo fibroblasts with ALV-J. Together, these results confirm that virulent chicken-derived ALV-J strains cannot infect geese, and that p27 antigen detection in goose serum is susceptible to non-specific interference.

A recombination efficiently increases the pathogenesis of the novel K subgroup of avian leukosis virus

In this study, a recombinant ALV with ALV-K env and ALV-J backbone was generated (designated ALV-K-env-J) and tested in vitro and in vivo. The growth curve in DF1 cells showed that the recombinant virus replicated more efficiently in comparison with the ALV-J and ALV-K. Although all the infected chickens showed growth retardation compared with the non-infected chickens, the viral and serological detection showed that the positive rate and virus load detected in blood and cloaca, and the positive rate and titer of antibody against p27 from the chickens infected with ALV-K-env-J were higher than those from the chickens infected with the ALV-K, but less than those from the chickens infected with the ALV-J. All these data clearly demonstrated that the recombination event in this study increased the pathogenesis of ALV-K, and the potential recombination between different ALV subgroups should be worried when the clinical co-infections occur.

Molecular characteristics of avian leukosis viruses isolated from indigenous chicken breeds in China

To assess the status of avian leukosis virus (ALV) infection in indigenous chicken breeds in China, 121 plasma samples collected from various indigenous chicken breeds were tested for the presence of ALV from 2015 to 2016. A total of 14 ALV strains were isolated and identified, including two ALV-A strains, one ALV-B strain, eight ALV-J strains, and three ALV-K strains. To study the genome structure, biological characteristics, and the evolutionary relationships of the ALV-K strains with other known subgroup strains from infected chickens, we determined the complete genome sequence of the three ALV-K strains and performed comparative analysis using the whole genome sequence or selected sequence elements. The replication rates of the three ALV-K strains were markedly lower than the rates of other ALVs, and they shared a common mutation in the pol gene, which had not been previously observed. In addition, nine putative recombinant events were detected in the genomes of the three newly isolated ALV-K strains, with high statistical support. This was the first report of an ALV-K reorganization event, which has contributed to its genetic evolution. In summary, we established a robust classification system for ALV, especially for ALV-K, and revealed additional genomic diversity for the ALV strains in indigenous chicken breeds. Therefore additional works are warranted to explore ALV genomics and epidemiology.

Phylogenetic Analysis and Pathogenicity Assessment of the Emerging Recombinant Subgroup K of Avian Leukosis Virus in South China

In recent years, cases of avian leukosis virus (ALV) infection have become more frequent in China. We isolated 6 ALV strains from yellow feather broiler breeders in south China from 2014 to 2016. Their full genomes were sequenced, compared, and analyzed with other reference strains of ALV. The complete genomic nucleotide sequences of GD150509, GD160403, GD160607, GDFX0601, and GDFX0602 were 7482 bp in length, whereas GDFX0603 was 7480 bp. They shared 99.7% to 99.8% identity with each other. Homology analysis showed that the gag, pol, long terminal repeats (LTRs), and the transmembrane region (gp37) of the env genes of the 6 viruses were well conserved to endogenous counterpart sequences (>97.8%). However, the gp85 genes displayed high variability with any known chicken ALV strains. Growth kinetics of DF-1 cells infected with the isolated ALV showed viral titers that were lower than those infected with the GD13 (ALV-A), CD08 (ALV-B), and CHN06 (ALV-J) on day 7 post-infection. The infected Specific-pathogen-free (SPF) chickens could produce continuous viremia, atrophy of immune organs, growth retardation and no tumors were observed. These subgroup ALVs are unique and may be common in south China. The results suggested that updating the control and eradication program of exogenous ALV for yellow feather broiler breeders in south China needs to be considered because of the emergence of the new subgroup viruses.

Characterization of Marek's disease virus and phylogenetic analyses of meq gene from an outbreak in poultry in Meghalaya of Northeast India

The aim of the present study was to characterize the virus from the lesions and histopathology of organs associated with mortality in Kuroiler (dual purpose variety of poultry developed and marketed by Keggfarms Pvt. Ltd, India) birds suspected of Marek's disease. Among 1047 birds from two farms of different location with 5.5 and 34% mortality, two types of lesion were observed in post mortem examination; tumors in vital organs-liver, spleen, kidney, lung and ovaries and generalized small nodular tumour in the abdominal cavity. Molecular characterization based on detection of ICP4 gene showed the presence of Marek's disease virus (MDV) from tissues and cell culture adapted isolates in Madin Darby Canine Kidney cell lines. Histopathological examination revealed multinucleated immature lymphoid cells infiltration in the organs. Phylogenetic analysis of the isolates based on meq gene showed the isolates belongs to cluster I genotype of MDV. This is for the first time the MDV virus is characterized from an outbreak in the poultry flock in farmer's field affecting production in Meghalaya state of North east India.

The construction and application of a cell line resistant to novel subgroup avian leukosis virus (ALV-K) infection

A novel avian leukosis viruses (ALV) subgroup named ALV-K was recently isolated from Chinese indigenous chickens which is different from the subgroups (A to E and J) that have previously been reported to infect chickens. More and more ALV-K strains have recently been isolated from local breeds of Chinese chickens. However, there are no more effective diagnostic methods for ALV-K other than virus isolation followed by envelope gene sequencing and comparison. Viral infection can be blocked through expression of the viral receptor-binding protein. In this study, we have engineered a cell line, DF-1/K, that expresses ALV-K env protein and thereby confers resistance to ALV-K infection. DF-1/K can be used in combination with the ALV-K susceptible cell line DF-1 as a specific diagnostic tool for ALV-K and provides a good tool for further research into the molecular mechanisms of interaction between ALV-K env protein and the host cell receptor.

Outbreak of Avian Tuberculosis in Commercial Domestic Pekin Ducks ( Anas platyrhynchos domestica)

Avian tuberculosis is a contagious disease affecting various domestic and wild bird species, and is caused by Mycobacterium avium . It is reported extremely rarely in commercial poultry flocks and has not been reported in commercial domestic ducks to date, with domestic ducks reported to be moderately resistant to M. avium infection. Here, we report the outbreak of avian tuberculosis in commercial Pekin duck ( Anas platyrhynchos domestica) flocks. Postmortem and histopathologic findings included nodules presenting in the visceral organs of ducks, and granulomas with central caseous necrosis surrounded by infiltrating lymphocytes. The M. avium pathogen was isolated and further identified by Ziehl-Neelsen staining and PCR based on insert sequence IS901 and the 16S rRNA gene. We highlight that avian tuberculosis not only has economic significance for the duck industry, but also presents a potential zoonotic hazard to humans.

A novel avian retrovirus associated with lymphocytoma isolated from a local Chinese flock induced significantly reduced growth and immune suppression in SPF chickens

Avian Leukosis Viruses (ALVs) are associated with neoplasias, immune suppression and reduced performance in chicken flocks. In the present study, a naturally occurring recombinant strain of ALV (FJ15HT0) was isolated from an infected flock of Chinese "Hetian" chickens, and was subsequently identified as an exogenous ALV by immuno-fluorescence assay (IFA), PCR and following entire proviral DNA nucleotide sequencing. This isolate is revealed as a novel recombinant virus, lacking viral oncogenes, with the gp85 (93.4%) of subgroup B, the U3 (92.1%) and R (95.2%) region of subgroup J, the U5 (93.8%) region and 5'UTR (95.7%) of subgroup C, as well as the gp37 (90.6%) and 3' (92.2%) of ALV-E. The simulative congenital infection with this isolate in SPF chickens resulted in significant weight loss (P<0.05) and a significant reduction in the humoral immune response to the live NDV vaccine (P<0.05), but not to the inactive AIV-H₅ vaccine (P>0.05). Foci of lymphocytomas were observed in tissues of congenitally infected chickens at 11 weeks post-hatch, demonstrating the acute oncogenicity of the isolate.

Isolation, identification and evolution analysis of a novel subgroup of avian leukosis virus isolated from a local Chinese yellow broiler in South China

Avian leukosis virus (ALV) causes high mortality associated with tumor formation and decreased fertility, and results in major economic losses in the poultry industry worldwide. Recently, a putative novel ALV subgroup virus named ALV-K was observed in Chinese local chickens. In this study, a novel ALV strain named GD14LZ was isolated from a Chinese local yellow broiler in 2014. The proviral genome was sequenced and phylogenetically analyzed. The replication ability and pathogenicity of this virus were also evaluated. The complete proviral genome sequence of GD14LZ was 7482 nt in length, with a genetic organization typical of replication-competent type C retroviruses lacking viral oncogenes. Sequence analysis showed that the gag, pol and gp37 genes of GD14LZ have high sequence similarity to those of other ALV strains (A-E subgroups), especially to those of ALV-E. The gp85 gene of the GD14LZ isolate showed a low sequence similarity to those other ALV strains (A-E subgroups) but showed high similarity to strains previously described as ALV-K. Phylogenetic analysis of gp85 also suggested that the GD14LZ isolate was related to ALV-K strains. Further study showed that this isolate replicated more slowly and was less pathogenic than other ALV strains. These results indicate that the GD14LZ isolate belongs to the novel subgroup ALV-K and probably arose by recombination of ALV-K with endogenous viruses with low replication and pathogenicity. This virus might have existed in local Chinese chickens for a long time.

Development, characterization and optimization of a new suspension chicken-induced pluripotent cell line for the production of Newcastle disease vaccine

Traditionally, substrates for production of viral poultry vaccines have been embryonated eggs or adherent primary cell cultures. The difficulties and cost involved in scaling up these substrates in cases of increased demand have been a limitation for vaccine production. Here, we assess the ability of a newly developed chicken-induced pluripotent cell line, BA3, to support replication and growth of Newcastle disease virus (NDV) LaSota vaccine strain. The characteristics and growth profile of the cells were also investigated. BA3 cells could grow in suspension in different media to a high density of up to 7.0 × 10(6) cells/mL and showed rapid proliferation with doubling time of 21 h. Upon infection, a high virus titer of 1.02 × 10(8) EID50/mL was obtained at 24 h post infection using a multiplicity of infection (MOI) of 5. In addition, the cell line was shown to be free of endogenous and exogenous Avian Leukosis viruses, Reticuloendotheliosis virus, Fowl Adenovirus, Marek's disease virus, and several Mycoplasma species. In conclusion, BA3 cell line is potentially an excellent candidate for vaccine production due to its highly desirable industrially friendly characteristics of growing to high cell density and capability of growth in serum free medium.

Development and application of SYBR Green I real-time PCR assay for the separate detection of subgroup J Avian leukosis virus and multiplex detection of avian leukosis virus subgroups A and B

Background

Subgroup A, B, and J ALVs are the most prevalent avian leukosis virus (ALV). Our study attempted to develop two SYBR Green I-based real-time PCR (RT-PCR) assays for specific detection of ALV subgroup J (ALV-J) and multiplex detection of ALV subgroups A and B (ALV-A/B), respectively.

Results

The two assays showed high specificity for ALV-J and ALV-A/B and the sensitivity of the two assays was at least 100 times higher than that of the routine PCR assay. The minimum virus detection limit of virus culture, routine PCR and real-time PCR for detection of ALV-A strain was 10³ TCID₅₀ units, 10² TCID₅₀ units and fewer than 10 TCID₅₀ units, respectively. In addition, the coefficients of variation for intra- and inter-assay were both less than 5%. Forty clinical plasma samples were evaluated by real-time PCR, routine PCR, and virus culture with positive rates of 80% (32/40), 72.5% (29/40) and 62.5% (25/40), respectively. When the assay for detection of ALV-J was used to quantify the viral load of various organ tissues in chicken inoculated by ALV-J strains CHN06 and NX0101, the results exhibited that ALV-J genes could be detected in all organ tissues examined and the highest copies of ALV-J were mainly in heart and kidney samples at 30 weeks post-infection. Except in lung, the virus copies of CHN06 group were higher than that of NX0101 group in various organ tissues.

Conclusions

The SYBR Green I-based real-time RT-PCR assay provides a powerful tool for the detection of ALV and study of virus replication and infection.

Further observations on serotype 2 Marek's disease virus-induced enhancement of spontaneous avian leukosis virus-like bursal lymphomas in ALVA6 transgenic chickens

Breeders of the 2009 generation of Avian Disease and Oncology Laboratory transgenic chicken line ALVA6, known to be resistant to infection with subgroups A and E avian leukosis virus (ALV), were vaccinated at hatch with a trivalent Marek's disease (MD) vaccine containing serotypes 1, 2, and 3 Marek's disease virus (MDV) and were maintained under pathogen-free conditions from the day of hatch until 75 weeks of age. Spontaneous ALV-like bursal lymphomas, also termed lymphoid leukosis (LL)-like lymphomas, were detected in 7% of the ALVA6 breeders. There was no evidence of infection with exogenous and endogenous ALV as determined by virus isolation tests of plasma and tumour tissue homogenates. For the next three generations, serotype 2 MDV was eliminated from the trivalent MD vaccine used. Results show, for the first time, that removal of serotype 2 MDV from MD vaccines eliminated spontaneous LL-like lymphomas within 50 to 72 weeks of age for at least three consecutive generations. Two experiments were also conducted to determine the influence of in ovo vaccination with serotype 2 MD vaccines on enhancement of spontaneous LL-like lymphomas in ALVA6 chickens. Chickens from the 2012 generation were each inoculated in ovo or at hatch with 5000 plaque-forming units of serotype 2 MDV. Results indicate that by 50 weeks of age the incidence of spontaneous LL-like lymphomas in chickens inoculated in ovo with serotype 2 MDV was comparable with that in chickens inoculated with virus at hatch, suggesting that the augmentation effect of serotype 2 MDV is independent of age of vaccination.

Preparation and immunoprotection of subgroup B avian leukosis virus inactivated vaccine

OBJECTIVES

To develop an inactivated vaccine against subgroup B avian leukosis virus (ALV-B) and determine if vaccination of chicken breeders could protect young chicks from ALV-B horizontal infection at early stage and accelerate eradication progress.

METHODS

Chicken embryo fibroblast (CEF) cells were inoculated with SDAU09C2 strain of ALV-B and ALV-CEF was inactivated for preparation of oil-adjuvant vaccine. Eggs were collected from un-vaccinated and 9 vaccinated great parent female chickens for incubation. 1-day-old chicks were bled for testing their maternal antibodies to ALV-A/B and then inoculated with ALV-B. Viremia and cloaca p27 detection dynamics were tested and compared between chick groups with or without maternal antibody to ALV.

RESULTS

In 3 weeks after 3 vaccination with the inactivated vaccine, all 9 vaccinated breeders developed high antibody titers against ALV-A/B with ELISA read values of 1.69-1.89 (the positive base line was 0.4) and kept at the high titers for at least another 4 weeks. Maternal antibody was detected in 70% (12/17) of chicks from breeders with high antibody titers to ALV-A/B. Only 4 of 12 chickens with maternal antibodies developed temporary viremia and no viremia was detected in the left 8 maternal antibody positive chickens during the whole 14 week after inoculation of ALV-B at 1 day of age. But the persistent viremia was detected in 2-8 weeks in all 9 maternal antibody negative chickens and the viremia persisted in the whole tested period of 14 weeks after inoculation of ALV-B.

CONCLUSIONS

The inactivated ALV-B vaccine could induce high titer antibody reaction to ALV-B, it could provide maternal antibodies to 1-day-old chickens and protect chickens from early infection of ALV-B.

Isolation, identification, and phylogenetic analysis of two avian leukosis virus subgroup J strains associated with hemangioma and myeloid leukosis

Cases of myeloid leukosis and hemangioma associated with avian leukosis virus subgroup J (ALV-J) are becoming more frequent in China in commercial layer chickens and breeders of egg-type chickens. In this study, two strains of ALV-J (SCAU11-H and SCAU11-XG) associated with hemangioma and myelocytoma were isolated from commercial broiler breeder animals in 2011. Their full-length proviral sequences were analyzed, revealing several unique genetic differences between the two isolates, and suggesting that the two viruses were derived from two distinct lineages. Strain SCAU11-H showed high sequence homology to early Chinese isolates associated with hemangioma, while strain SCAU11-XG was genetically closer to the prototype strain, HPRS-103. The complete genomic nucleotide sequences of SCAU11-H and SCAU11-XG were 7471 bp and 7727 bp in length, respectively. They shared 94.8% identity with each other, and had 94.0-96.8% nucleotide identity to ALV-J reference isolates. Homology analysis of the env, pol, and gag genes of the two isolates and other references strains showed that the gag and pol genes of the two viruses were more conserved than the env gene. In addition, the two isolates had significant deletions and substitutions in their 3'-UTR regions, compared to HPRS-103. These results suggest that the env gene and the 3'-UTR regions in these ALV-J isolates have evolved rapidly, and might be involved in the oncogenic spectrum of ALV-J. The results of this study contribute to our further study of the relationship between ALV integration patterns and multi-pathotypes associated with ALV-J.

Avian leukosis virus subgroup J associated with the outbreak of erythroblastosis in chickens in China

Background

Emaciation, depression and lethargy were observed in two flocks of Chinese local breed and one flock of commercial layer chicken infected naturally from 2010 to 2011. The aims of this study were to diagnose.

Methods and results

Gross observation showed that severe enlargement of liver, spleen and kidney, and hemorrhage of thymus, muscle and glandular stomach in all submitted birds. The liver and lung of one flock had diffuse, multifocal white raised foci on the surface as well as on the cut-surface. Numerous erythrocytoblasts with bigger volume, basophilic cytoplasm and round nucleus were observed in blood and bone marrow smears. The same erythrocytoblasts were also found crowded in blood vessels and mesenchym of tissues by histological examination, and some had mitotic figures. PCR results showed that three flocks were positive for ALV-J with specific fragment of 924 bp, negative for AEV, ALV-A, ALV-B, Marek’s disease virus (MDV) and Reticuloendotheliosis virus (REV). The results of immunohistochemistry showed that cytoplasm of histiocytes and erythrocytoblasts in lung and spleen sections was positive for ALV-J antigen.

Conclusion

These data demonstrated that erythroblastosis was all induced by ALV-J in the three different flocks. This is the first document report of erythroblastosis induced by ALV-J in China flocks.

Development of an antigen-capture ELISA for the detection of avian leukosis virus p27 antigen

An antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) employing monoclonal and polyclonal antibodies against p27 was developed for the detection of the avian leukosis virus (ALV). The specificity of the optimized AC-ELISA was evaluated using avian leukosis virus subgroup J (ALV-J), avian leukosis virus subgroup A (ALV-A), avian leukosis virus subgroup B (ALV-B), avian infectious bronchitis virus (IBV), Marek's disease virus (MDV), avian infectious laryngotracheitis virus (ILTV), Fowlpox virus (FPV), infectious bursal disease virus (IBDV), Newcastle disease virus (NDV), avian reovirus (ARV), reticuloendotheliosis virus (REV), avian influenza virus (AIV) and Escherichia coli. The only specimens that yielded a strong signal were ALV-J, ALV-A and ALV-B, indicating that this assay is suitable for the detection of ALV. The limit of detection of this assay was 1.25 ng/ml of rp27 protein and 10(1.79)TCID(50) units of HLJ09MDJ-1 (ALV-J). Moreover, this AC-ELISA can detect ALV in cloacal swabs of chickens experimentally infected as early as 12 days post-infection. The AC-ELISA detected the virus in the albumin and cloacal swabs of naturally infected chickens, and the results were confirmed by PCR, indicating that the AC-ELISA was a suitable method for the detection of ALV. This test is rapid and sensitive and could be convenient for epidemiological studies and eradication programs.

Development and application of real-time PCR for detection of subgroup J avian leukosis virus

Subgroup J avian leukosis virus (ALV-J) is an avian retrovirus that causes severe economic losses in the poultry industry. The early identification and removal of virus-shedding birds are important to reduce the spread of congenital and contact infections. In this study, a TaqMan-based real-time PCR method for the rapid detection and quantification of ALV-J with proviral DNA was developed. This method exhibited a high specificity for ALV-J. Moreover, the detection limit was as low as 10 viral DNA copies. The coefficients of variation (CVs) of both interassay and intra-assay reproducibility were less than 1%. The growth curves of ALV-J in DF-1 cells were measured by real-time PCR, yielding a trend line similar to those determined by 50% tissue culture infective dose (TCID(50)) and p27 antigen detection. Tissue samples suspected of ALV infection were evaluated using real-time PCR, virus isolation, and routine PCR, and the positivity rates were 60.1%, 41.6% and 44.5%, respectively. Our data indicated that the real-time PCR method provides a sensitive, specific, and reproducible diagnostic tool for the identification and quantification of ALV-J for clinical diagnosis and in laboratory research.

Differential detection of avian oncogenic viruses in poultry layer farms and Turkeys by use of multiplex PCR

Avian oncogenic viruses include Marek's disease virus (MDV), a highly contagious herpesvirus, as well as retroviruses such as avian leukosis virus (ALV) subgroups A to J and reticuloendotheliosis virus (REV). In this study, we examined the incidence of these viruses in suspected samples collected from poultry layer farms of South India, mainly in the Namakkal district of Tamil Nadu, a highly dense poultry-growing area in India. The histopathology-positive tissue sections were identified and further confirmed by immunohistochemistry using virus-specific antibodies. The viruses belonging to all 3 groups (MDV, ALV, and REV) were isolated in a cell culture system and confirmed by immunofluorescence using virus-specific antibodies. PCR appeared to be the method of choice for rapid and accurate diagnosis of these viruses. The multiplex PCR primers specific to MDV, ALV, REV, and chicken DNA were designed for rapid differential diagnosis. The specificity of the primers was checked by amplification of DNA from virus-infected cell culture in comparison with uninfected samples, and sensitivity was evaluated by calculating the minimum copy number at which amplification occurs in the cloned PCR products. The sequences of the amplicons were compared by BLAST analysis. PCR tests demonstrated the presence of single, dual, or triple viruses in some of the samples. Of 169 samples screened by multiplex PCR, 9 samples were positive for MDV, 17 samples were positive for ALV, 12 samples were positive for REV, and 17 samples were positive for both ALV and REV. Three samples were positive for all three viruses. ALV-positive samples were further subjected to subgroup-specific PCR, which gave positive results for subgroups B and D but not for subgroup J. Multiplex PCR appeared to be a useful technique for rapid differential diagnosis of avian oncogenic viruses and detection of multiple infections of avian oncogenic viruses under field conditions.

Development and validation of an indirect enzyme-linked immunosorbent assay for the detection of Avian leukosis virus antibodies based on a recombinant capsid protein

Avian leukosis virus (ALV) is associated with tumor development and growth retardation in poultry. Eradication of virus infection at the primary breeder level is the principal method for controlling ALV infection in chickens. An indirect enzyme-linked immunosorbent assay (iELISA) method that utilized the prokaryotically expressed and affinity-purified viral capsid protein antigen p27 was developed for the detection of ALV-specific antibodies in chicken sera. The protocol of iELISA was validated and resulted in a higher agreement value than fluorescent antibody test (FAT) and was shown to be more sensitive and specific compared to the commercial ALV antibody test kit when FAT was used as a reference test. The main advantage of this method is the use of a single immunogenic protein to detect antibodies against all ALV exogenous subgroups. The results show that the developed iELISA is an inexpensive alternative and can potentially be used as a confirmatory test for the presence of anti-ALV antibodies on a large scale.

Molecular identification of avian leukosis virus subgroup E loci and tumor virus B locus in Chinese indigenous chickens

Avian leukosis virus (ALV) subgroup E (ALVE) is an endogenous retrovirus in the chicken genome. The chickens carrying ALVE locus 3 (ALVE3), 6 (ALVE6), 9 (ALVE9), and 21 (ALVE21) have been proved to be susceptible to ALV. Tumor virus locus B (TVB) encodes the cellular receptor for ALV subgroups B, D, and E. The insertions of the 4 ALVE loci and the genotypes of TVB have not been demonstrated in Chinese indigenous chicken breeds. In the present study, the existence of ALVE3, ALVE6, ALVE9, and ALVE21 were detected in 10 native breeds of Chinese chickens and an introduced breed, the White Leghorn (2 populations in this study, WL1 and WL2), by locus-specific PCR. The PCR products of ALVE were further confirmed by sequencing assay. We also surveyed the status of genotypes of TVB in Silkie, Beijing You, and White Leghorn (WL1 and WL2) chickens with pyrosequencing assays. The results showed that the carrier frequency of ALVE3 was 1.3% in the Chinese chicken population, and was 10.3 in WL1 and 49.2% in WL2. The carrier frequency of ALVE6 was 5.4% in native breeds of Chinese birds, in contrast with 0% in WL1 and 6.8% in WL2. The carrier frequency of ALVE9 was 0.1% in the Chinese indigenous population, and was 16.0% in WL1 and 11.9% in WL2. The carrier frequency of ALVE21 was 10.4% in Chinese chickens, whereas ALVE21 was detected with a frequency of 0% in WL1 and 50% in WL2. The frequency of the TVB resistance allele (TVB*R and TVB*R') was 0.4% in Beijing You chickens, whereas it was 70.5% in WL1 and 54.5% in WL2. No carriers of ALVE3, ALVE9, and ALVE21 were detected in Silkie fowl, a famous Chinese native breed that has been used as a source for alternative medicine. These results present molecular evidence of ALVE3, ALVE6, ALVE9, and ALVE21 insertions and TVB genotypes in Chinese indigenous chickens and could provide potential molecular insights into anti-ALV breeding in chickens.

Detection of avian leukosis virus subgroups in albumen of commercial and native fowl eggs using RT-PCR in Iran

Avian leukosis viruses (ALVs) belong to Alpharetrovirus genus of the family Retroviridae that are widespread in nature. Different subgroups of ALV commonly infect egg-laying hens. They are responsible for economic losses due to both mortality and depressed performance in chickens. To investigate the presence of these viruses in chickens in Iran, 560 egg albumens were selected from different farms of Fars province, Iran. These eggs were obtained from flocks of two research centers of native fowl production (60 eggs), a broiler grandparent farm (100 eggs), three broiler breeder farms (300 eggs), and a commercial layer flock (100 eggs). Firstly, for primary screening a degenerative primer set (PU1 and PU2) were used in reverse transcriptase-polymerase chain reaction (RT-PCR). Positive cases were detected in 47 of 300 (15.7%) samples from three broiler breeders, 40 of 100 (40%) samples from commercial layer, 53 of 60 (88.3%) samples from flocks of two research centers of native fowl production, and none from the samples of broiler grandparent. Then RT-PCR was undertaken with primers PA1 and PA2 on the positive samples. RT-PCR analysis detected ALVs in two of 47 (4.3%) samples from three broiler breeders, 13 of 40 (32.5%) samples from commercial layer, and 19 of 53 (35.8%) samples from flocks of two research centers of native fowl production. The sequencing results showed that subgroup E of ALV was the most detected virus among chicken eggs and subgroup B was more prevalent in the eggs of native fowls. This is the first report of the ALV subgroup B and E in egg albumen in Iran.

Tumors associated with avian leukosis virus subgroup J in layer hens during 2007 to 2009 in China

In the 3 years leading up to November 2009, 6 different types of naturally occurring neoplasms associated with avian leukosis virus subgroup J (ALV-J) were diagnosed by histopathology, polymerase chain reaction (PCR) and immunohistochemistry (IHC) in 140 layer hens out of approximately 100,000. The most prevalent tumor type was hemangioma (50%) in commercial layer flocks; the second most prevalent neoplasm type was myelocytoma (38.6%); a small number of ALV-J positive lymphomas (4.3%) that were not associated with Marek's disease (MD) or lymphoid leukosis (LL) was observed. Histiocytic sarcomas (2.1%) were found mainly in the spleen, liver and kidney. Fibrosarcomas (2.8%) presented as metastatic thigh, liver, lung and kidney neoplasms. Three cases of intestinal adenocarcinoma (2.1%) were found associated with ALV-J. Chickens with multiple tumors were a common phenomenon. Usually, hemangiomas plus myelocytomas (8.6%), myelocytomas plus histiocytic sarcomas (2.1%), hemangioma plus myelocytoma and lymphoma (3.6%) were found in various viscera organs. The present report describes the occurrence of multiple neoplasms associated with ALV-J in field layer hens.

Isolation and identification of a subgroup A avian leukosis virus from imported meat-type grand-parent chickens

An exogenous avian leukosis virus (ALV) strain SDAU09C1 was isolated in DF-1 cells from one of 240 imported 1-day-old white meat-type grand parent breeder chicks. Inoculation of SDAU09C1 in ALV-free chickens induced antibody reactions specific to subgroup A or B. But gp85 amino acid sequence comparisons indicated that SDAU09C1 fell into subgroup A; it had homology of 88.8%-90.3% to 6 reference strains of subgroup A, much higher compared to other subgroups including subgroup B. This is the first report for ALV of subgroup A isolated from imported breeders.

Development of a loop-mediated isothermal amplification assay for rapid detection of subgroup J avian leukosis virus

Infection of breeder flocks in China with subgroup J avian leukosis virus (ALV-J) has increased recently. In this study, we have developed a loop-mediated isothermal amplification (LAMP) assay for rapid detection of ALV-J from culture isolates and clinical samples. The ALV-J-specific LAMP assay efficiently amplified the target gene within 45 min at 63 degrees C using only a simple laboratory water bath. To determine the specificity of the LAMP assay, various subgroup ALVs and other related viruses were detected. A ladder pattern on gel electrophoresis was observed for ALV-J isolates but not for other viruses. To evaluate the sensitivities of the LAMP assay and conventional PCR, the NX0101 isolate plasmid DNA was amplified by them. The detection limit of the LAMP assay was 5 target gene copies/reaction, which was up to 20 times higher than that of conventional PCR. To evaluate the application of the LAMP assay for detection of ALV-J in clinical samples, 49 samples suspected of ALV infection from breeder flocks were tested by the LAMP assay and PCR. Moreover, virus isolation from these samples was also performed using cell culture. The positive-sample ratios were 21/49 (43%) by conventional PCR, 26/49 (53%) by the LAMP assay, and 19/46 (41%) by virus isolation. Additionally, a positive LAMP reaction can be visually ascertained by the observation of turbidity or a color change after addition of SYBR green I dye. Consequently, the LAMP assay is a simple, rapid, and sensitive diagnostic method and can potentially be developed for rapid detection of ALV-J infection in the field.

Survey of endogenous virus and TVB* receptor status of commercial chicken stocks supplying specific-pathogen-free eggs

Endogenous avian leukosis virus (ALVE) and the ALVE receptor (TVB*S1) status of six commercial chicken lines supplying specific-pathogen-free eggs were analyzed. All commercial chicken lines are certified free of the avian leukosis virus (ALV) by screening for expression of the p27 protein using the standard enzyme-linked immunosorbent assay. The commercial chicken lines A, E, and F contained replication competent ALVE inserts. Line A was fixed for ALVE21, and lines E and F were segregating for ALVE10. In addition, ALVE1 was detected in all the chicken lines. Chicken lines B, D, and F were essentially fixed for the TVB*S1 allele that confers susceptibility to ALVE, whereas lines A, C, B, and E were resistant, containing either the TVB*S3 or TVB*R alleles. The results show that lines selected to be ALV p27 negative give rise to two different genotypes. One genotype lacks the TVB*S1 receptor for ALVE. Chicken lines with the TVB*S1 negative genotype can retain replication competent endogenous virus inserts such as ALVE2, 10, or 21 and still display the p27 negative phenotype. These replication competent ALVE viruses are phenotypically p27 negative in the absence of the TVB*S1 receptor because their chromosomal integration sites restrict transcription and subsequent production of the p27 protein and virus particles to levels below the detection limit. If the TVB*S1 receptor is present, the limited production of ALVE virus particles reinfects and integrates into more productive chromosomal locations in the cell. Increased production of infective virus particles and detectable levels of p27 follow this reinfection and integration into more active regions of the cells genome. The other genotype observed in the commercial lines retains the ALVE receptor (TVB*S1) but either lacks replication competent inserts or expresses the envelope encoded protein from defective inserts such as ALVE3 or ALVE6. In this phenotype, the env-coded glycoprotein encoded by the defective inserts binds to the TVB*S1 receptor and blocks the reinfection of the replication competent ALVE virus. This receptor interference stops reinfection and subsequent production of detectable virus particles and the p27 protein. Mixtures of different p27 negative phenotypes can result in the p27 positive phenotype and ALVE virus production. For example, mixtures of ALVE receptor positive (TVB*S1) but ALVE negative (p27 negative and envelope negative) chick embryo fibroblasts (CEFs) with fibroblasts that are receptor negative but ALVE positive could generate cells expressing high levels of p27 and ALVE virus. In this situation, the undetectable levels of ALVE virus from the receptor negative CEFs would infect and integrate into the receptor positive CEFs and produce detectable levels of ALVE virus. The implications of these findings for vaccine manufacturers and regulatory agencies are discussed.